A conventional apparatus for reclamation of molding sand has been known, such as one disclosed in Japanese Patent No. 3125276. It comprises a chute for falling sand. The chute has a sand falling port at its bottom. The apparatus comprises a rotary drum, which is disposed below the chute and rotatable horizontally. It has an inclined circumferential wall extending from a circular bottom plate to the upper-outward direction. A ring portion (gate) extends inwardly from the upper end of the inclined circumferential wall. The apparatus also comprises a roller, which is disposed horizontally in the rotary drum and slightly spaced apart from the inclined circumferential wall. It also comprises a mechanism for pressing the roller toward the inclined circumferential wall by a predetermined pressure.
It employs a system to remove deposit from the surfaces of sand by pressing the sand by the roller. The sand is continuously fed into the rotary drum and is piled on the inner surface of the inclined circumferential wall of the drum by centrifugal force. The roller presses the piled sand to remove its deposit.
Because it has no function to control the pressure of the roller, the properties of the sand vary widely depending on the production line. When the flow of the sand fed into the apparatus changes, the current of a motor for driving the rotary drum changes. Thus, if the driving force of the motor is not appropriate to the flow of the sand, it is difficult to maintain an adequate quality of the molding sand reclaimed by the apparatus.
At the same time, a method of controlling the operation of a vertical crushing machine is proposed in Japanese Patent Application No. 2000-126633. In the method, at any time a specific pressure is monitored. The specific pressure is the ratio of the pressure applied from the crushing roller to the turntable to the thickness of raw materials between the crushing roller and the turntable. When the amount of supplied raw materials to the turntable changes, the specific pressure is controlled to be uniform by comparing the monitored specific pressure to a predetermined one. By doing so, the vibrations of the machine are reduced and the desired grain sizes are efficiently obtained.